1. Field of the Invention
The present invention is generally related to a compact, low resistance, effective sound attenuator and, more particularly, to a sound attenuator intended for use with a marine propulsion device, such as an outboard motor and tuned for a selected range of frequencies.
2. Description of the Prior Art
Many types of devices produce sound at frequencies and amplitudes that can be annoying or discomforting to human beings in the vicinity of the device when it is operating. For example, automobile engines use mufflers to reduce the level of sound emanating from the internal combustion engine of the automobile. Many applications of compressors use mufflers, or sound dampers, to limit the magnitude of sound emanating from the compressor. When a compressor or Roots blower is used as a supercharger in conjunction with an internal combustion engine, significant sound naturally emanates from the compressor or blower. It is therefore useful to provide a sound attenuation device in combination with a compressor.
U.S. Pat. No. 4,192,401, which issued to Deaver et al on Mar. 11, 1980, describes a complete louver flow muffler. A muffler for reducing the audible noise level of exhaust gases emitted by combustion engines has an inlet tube with a patch of louvers or perforations and is arranged so that all or substantially all of the gas flowing through the muffler is forced through the patch into an expansion chamber from which it flows by either cross bleeding through a patch of louvers or perforations into an outlet tube or to a chamber opening into the inlet end of the outlet tube. A splitter partition may be used to control flow through the louvers and provide additional attenuation. An imperforate portion of the inlet tube is used as a driven tuning tube with a resonator chamber to form a Helmholtz low frequency attenuation system, the performance of which may be improved in some cases by use of an orifice in a wall of the resonator. Also disclosed is a muffler in which all of the gas flows through a louver patch in the outlet tube and an imperforate part of the outlet tube is used as a part of an aspirating type Helmholtz system.
U.S. Pat. No. 3,993,160, which issued to Rauch on Nov. 23, 1976, describes a silencer for a heat engine. An outer return tube is provided outside an exhaust silencer case and forms part of means for interconnecting the downstream end of an upstream tube and the upstream end of a downstream tube with respect to the direction of travel of the exhaust gases through the silencer. The upstream tube and downstream tube are perforated and extend in the case. At least a fraction of the exhaust gas stream travels through the outer return tube.
U.S. Pat. No. 6,408,832, which issued to Christiansen on Jun. 25, 2002, discloses an outboard motor with a charge air cooler. An outboard motor is provided with an engine having a screw compressor which provides a pressurized charge for the combustion chambers of the engine. The screw compressor has first and second screw rotors arranged to rotate about vertical axes which are parallel to the axes of crankshaft of the engine. A bypass valve regulates the flow of air through a bypass conduit extending from an outlet passage of the screw compressor to the inlet passage of the screw compressor. A charge air cooler is used in a preferred embodiment and the bypass conduit then extends between the cold side plenum of the charge air cooler and the inlet of the compressor. The charge air cooler improves the operating efficiency of the engine and avoids overheating the air as it passes through the supercharger after flowing through the bypass conduit. The bypass valve is controlled by an engine control module in order to improve power output from the engine at low engine speeds while avoiding any violations of existing limits on the power of the engine at higher engine speeds.
U.S. Pat. No. 6,405,692, which issued to Christiansen on Jun. 18, 2002, discloses an outboard motor with a screw compressor supercharger. An arrangement similar to that described above in relation to U.S. Pat. No. 6,408,832, is provided.
U.S. Pat. No. 6,382,931, which issued to Czabala et al on May 7, 2002, describes a compressor muffler. A muffler assembly for muffling noises associated with a compressor is described. The muffler assembly is mounted on the compressor such that the two move as a single body. The muffler assembly includes an intake having a hollow interior adapted to receive a first flow of gas from the ambient environment. A baffle disposed in the hollow interior of the intake restricts the flow of gas through the intake. In one embodiment, the baffle defines at least a portion of a plurality of fluid portals that separate the first flow of gas into a plurality of flows of gas as the gas passes from a first side of the baffle to a second side of the baffle. As a result, the first flow of gas is disturbed and noise from the compressor is thereby attenuated. In another embodiment, a plurality of baffles are disposed in the hollow interior of the intake to define a tortuous path for the flow of gas through the intake for attenuating noise.
U.S. Pat. No. 6,361,290, which issued to Ide on Mar. 26, 2002, describes a suction muffler for a hermetic compressor. The invention provides a suction muffler comprising component portions formed by injection forming a thermoplastic synthetic resin and joined to each other by induction welding, and also provides a hermetic compressor including the suction muffler. The suction muffler having this configuration is superior to conventional suction mufflers having joint portions joined by ultrasonic welding and vibration welding in the uniformity of the welding strength at the whole joint portion thereof and in minimizing the occurrence of fins.
U.S. Pat. No. 6,287,098, which issued to Ahn et al on Sep. 11, 2001, describes a muffler for a rotary compressor. A rotary compressor including a main bearing having a discharge passage for discharging compressed gas and a boss for inserting a motor shaft is described. The main bearing forms a component of a compression chamber and a muffler has a boss hole for passing the boss of the main bearing and a discharge opening for discharging the compressed gas. The muffler is mounted on the main bearing, wherein the discharge opening in the muffler is formed at least one in number inside of the discharge passage in the main bearing, whereby attenuating a noise generated in operation of the rotary compressor is effectively accomplished.
U.S. Pat. No. 6,129,522, which issued to Seo on Oct. 10, 2000, describes a suction muffler for a compressor. The suction muffler has a body and suction pipe. The body has an expansion chamber for expanding gaseous refrigerant flowing from an evaporator, a suction chamber for drawing the refrigerant expanded in the expansion chamber, and a resonance chamber in which the refrigerant drawn into the suction chamber resonates. The suction pipe is assembled with the body and connects the suction chamber with a cylinder head of the compressor. The suction pipe provides a passage that the refrigerant in the suction chamber flows into the cylinder head. The refrigerant flows into the suction chamber after being expanded in the expansion chamber, so the noise caused by the pulsation of pressure is reduced and the refrigerant resonating in the resonance chamber can reduce the noise of a specific frequency. Further, since the suction muffler has a simple construction having a small number of components, the leakage of noise through the gaps between the components can be reduced.
U.S. Pat. No. 5,996,731, which issued to Czabala et al on Dec. 7, 1999, describes a compressor muffler. A muffler assembly for muffling noises associated with a compressor is described. The muffler assembly includes an air intake having a hollow interior for receiving air from the ambient environment when the compressor is operating. A baffle is located within the interior of the intake for restricted passage of the air through the intake. A fluid portal is defined within the baffle for enabling fluid to pass from one side of the baffle to the other side of the baffle and subsequently through the air intake. An attenuator is disposed within the fluid portal for attenuating noise and the attenuator disturbs the sound waves associated with the operation of the compressor.
U.S. Pat. No. 5,938,411, which issued to Seo on Aug. 17, 1999, describes a compressor noise reducing muffler. A noise reducing muffler for a compressor includes a base muffler and a suction muffler connected to an upper end of the base muffler. Gaseous coolant flows through the suction muffler and the base muffler and into a cylinder head of a compressor. The suction muffler defines a path of travel wherein all of the gaseous coolant flows vertically downwardly, then horizontally, and then vertically downwardly to the base muffler.
U.S. Pat. No. 5,605,447, which issued to Kim et al on Feb. 25, 1997, describes noise reduction in a hermetic rotary compressor. The invention concerns a noise reduction method and a noise reduction device for a hermetic rotary compressor. It is designed to reduce the very high level of low frequency sound generated by the compressor by preventing the formation of reflected waves along the circumference which produce the resonant sound mode and thus by preventing the amplification of the low frequency gas pulsations. In the invention, the amplitude of the reflected waves that form the resonant sound mode is reduced by installing the muffler outlets at one half the wavelength of the reflective waves the cavity of the compressor housing from the exhaust valve where the compressed gas from the cylinder enters the muffler. By positioning these outlets face each other so that the pulsating gas components form two outlets, those at the frequency of the reflected waves formed in the circumferential direction of the cavity of the compressor housing will undergo a 180xc2x0 phase shift and destructively interfere with each other.
U.S. Pat. No. 5,584,674, which issued to Mo on Dec. 17, 1996, describes a noise attenuator of a compressor. A noise attenuator for a refrigerant circulating compressor includes a casing whose interior space is divided into first the second chambers. The first chamber has an inlet for receiving refrigerant and is connected by a conduit with the second chamber. Additional conduits connect the second chamber with the compressor inlet. The cavity length L of the first chamber is determined as a function of a compressor noise to be attenuated. The first chamber may comprise a first portion and a second portion in the form of a branch line, with the cavity length L begin defined by a combination of both of the portions.
U.S. Pat. No. 5,260,524, which issued to Schroeder et al on Nov. 9, 1993, describes a muffler for an air compressor. A noise reduction method using a muffler for connection to the air inlet of an air compressor including an imperforate, hollow housing enclosed in a chamber, air inlet and outlet openings in the housing, an air inlet tube in the housing connected to the air inlet opening and an air outlet tube in the housing connected to the air outlet opening, both tubes extending over half the length of the chamber, and the openings of the distal ends of the tubes facing in the opposite directions.
U.S. Pat. No. 5,220,811, which issued to Harper et al on Jun. 22, 1993, describes a suction muffler tube. A muffler tube for use in a hermetically sealed compressor is disclosed. The muffler tube of the present invention has a roughened outer finish, and has a protuberance extending radially outwardly therefrom. The protuberance is received in a recess in the inner wall of the muffler. The combination of the roughened outer finish and the protuberance connection assist in preventing the muffler from turning on the tube and from moving vertically on the tube.
U.S. Pat. No. 5,136,923, which issued to Walsh, Jr. on Aug. 11, 1992, describes a firearm silencer and flash attenuator. A firearm sound suppressor includes an outer housing, an interior perforated tube located within the outer housing, and spacing between the outer housing and interior perforated tube. The sound suppressor is adapted to be mounted on a firearm.
U.S. Pat. No. 5,679,916, which issued to Weichert on Oct. 21, 1997, describes a gun silencer. A silencer for a firearm is disclosed as comprising a composite outer wall, an end piece which forms a silencer muzzle and in which is located an exit opening, an attachment piece which is attached to the end piece, and a middle piece which is positioned between the attachment piece and the end piece. The middle piece comprises a selected number of successive chambers which are aligned with each other. Each of the chambers has a firing opening and an outside wall. Each of the chambers is attached in a modular fashion directly to an adjoining one of the selected number of chambers. The outside walls of the selected number of chambers form the composite silencer wall. The number of silencers is selected in accordance with the intended use of the silencer.
U.S. Pat. No. 4,576,083, which issued to Seberger, Jr. on Mar. 18, 1986, describes a device for silencing firearms. A cylindrical silencer tube is fastened to a muzzle of a firearm. The interior of the tube is equipped with a series of chambers and conically shaped baffles which direct part of the discharge gases and sound waves in a different path from the main discharge and then causes them to reunite before they discharge the silencer at a point where part of the sound waves have been delayed and are hence out of phase with the principal waves and cause elimination of the noise. Specially constructed inlet and outlet chambers within the tube aid in the suppression of the sound waves and deafening of the noise. The exterior of the cylindrical silencer tube is equipped with a series of cooling fins to aid in the dissipation of heat from the silencer.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In certain applications, it is critically important that the sound attenuating device be compact and require a minimum amount of space. It is also very important in certain applications that the sound attenuating device be as minimally restrictive to air flow as possible. These characteristics are particularly important in applications such as marine propulsion devices, where the sound attenuator device must be contained within a restricted space, such as under the cowl of an outboard motor. Also, in an outboard motor application, it is important that the sound attenuating device not inhibit the free flow of air into the compressor.
It would therefore be significantly beneficial if a sound attenuating device could be provided which requires minimal space and which provides very little resistance to the free flow of air through the device as it passes to a compressor and, eventually, to the intake manifold of an internal combustion engine.
A sound attenuator for a supercharged marine propulsion device, made in accordance with the preferred embodiment of the present invention, comprises an airflow conduit having an inlet end and an outlet end. In certain applications, the outlet end is connectable in fluid communication with an inlet conduit of a compressor. A first chamber is disposed proximate a first portion of the airflow conduit. The first chamber has a first length. A first plurality of holes is formed through the first portion of the airflow conduit, with the first plurality of holes being in fluid communication between the airflow conduit and the first chamber. The first length and the size of each of the first plurality of holes are selected to be compatible with each other in reflecting a first range of frequencies of sound, which are passing in a direction from the outlet end toward the inlet end of the airflow conduit, back toward the outlet end of the airflow conduit. A second chamber is disposed proximate a second portion of the airflow conduit and has a second length. A second plurality of holes if formed through the second portion of the airflow conduit, with the second plurality of holes being in fluid communication with the airflow conduit and the second chamber. The second length and the size of each of the second plurality of holes are selected to be compatible with each other in reflecting a second range of frequencies of sound, which are passing in a direction from the outlet end toward the inlet end of the airflow conduit, back toward the outlet end of the airflow conduit.
The compressor has the inlet conduit and an outlet conduit and an associated internal combustion engine has an air intake conduit. The outlet conduit of the compressor is connected in fluid communication with the intake conduit of the internal combustion engine.
The first and second chambers, define first and second annular cavities surrounding the first and second portions of the airflow conduit, respectively. The first and second annular cavities are generally coaxial with the first and second airflow conduits, respectively. The first and second plurality of holes extend radially through the first and second portions of the airflow conduit, respectively.